Are you going to buy a camera, or build it yourself?
Are you going to buy image capture s/w, or build it yourself?
and so on.

For stuff you intend to build, you need to start breaking the problem down into smaller and smaller steps, until you arrive at something sufficiently detailed you can implement in code.

For stuff you intend to buy, you need to write requirements (cost, performance, durability (does it need to be weatherproof say), supported platforms, etc etc) so you can purchase the appropriate bit of kit that will do the job you have in mind.

salem gave you the best advice. scorpions pointed you to another similar request.

Just what exactly do you expect? Even if I had retinal-scan code in my back pocket, such code would be very dependent on the equipment that you're having it run, so any loose code we just happen to have lying around would most likely not work for you.

Now, if you had followed salem's advice, you would know what hardware you're going to use. Many hardware products include software development kits which show you how to write programs that will work with that hardware. Some manufacturers will even have sample code on their websites.

And when all else fails, hire a programmer who has experience writing retinal scan software! This is non-trivial software that you're asking for. You can't expect to get it for free.